The recent growing awareness of environmental issue has brought forth a requirement that no poisonous gases such as halogen-based gas be emitted during combustion. Referring to insulated wire for an automobile, it has been practiced to apply a non-halogen-based resin composition having a metal hydrate incorporated in a polyolefin-based resin as an insulating material. However, it is necessary that this non-halogen-based resin composition comprises a large amount of a metal anhydride incorporated therein to have the same fire retardancy as halogenic fire retardant materials. This arrangement results in the deterioration of flexibility, abrasion resistance, low temperature properties and mechanical strength of tensile strength and tensile elongation at break. It has thus been required that the fire retardancy and the mechanical strength of the fire retardant material be well balanced.
To cope with this problem, fire retardant olefinic resin compositions comprising a low crystallinity flexible α-olefinic homopolymer or copolymer and magnesium hydroxide have been proposed as in JP-A-62-167339. This approach is intended to fill the homopolymer or copolymer with magnesium hydroxide in a high packing, thereby producing a composition having a high fire retardancy as well as excellent flexibility, low temperature properties and workability. However, even this composition leaves something to be desired in abrasion resistance and heat resistance and thus is still disadvantageous in practicability.
Further, JP-A-5-239281 proposes an abrasion-resistant fire retardant composition made of a polymer comprising an α-olefin (co)polymer, ethylene (co)copolymer or rubber, an inorganic fire retardant, a carboxylic acid group, etc. However, even this composition exhibits an excellent fire retardancy and flexibility but leaves something to be desired in heat resistance and abrasion resistance because it comprises an ethylene (co)polymer or rubber as an essential component.
Moreover, JP-2000-26696 proposes a fire retardant resin composition comprising a propylene-ethylene block copolymer, a thermoplastic polyolefin-rubber elastomer and a metal hydroxide. However, even this composition leaves something to be desired in abrasion resistance because it comprises a thermoplastic polyolefin-rubber elastomer as an essential component.
The invention has been worked out under these circumstances. An object of the invention is to provide a wire for an automobile comprising an insulating layer made of a polypropylene-based resin composition, wherein a fire retardancy comparable to that of the related halogen-based fire retardant materials is obtained, and the mechanical properties such as abrasion resistance, tensile strength and elongation, flexibility, low-temperature flexing, heat resistance and chemical resistance are improved.